While from a strictly scientific point of view it is impossible to tell
if a mollusc was albinistic just by looking at a shell (and sometimes an
animal which has an unpigmented body will produce a pigmented shell!),
most collectors will consider a completely white (no trace of
pigmentation) shell of any species that is very seldom white (some
species are normally white, or have a white color morph that turns up
frequently - these cannot be "conchologistically" albino, in terms of
being worth more because of their unpigmented condition), is termed
"albino".  Shell collecting is not always a completely science-oriented activity!!

From Summer-at-last New Scotland (most likely Fall City next week tho!),
Ross.